:root{
  --bg:#f4f5f2; --surface:#ffffff; --ink:#1d2640; --muted:#5b6377; --line:#dde0e5;
  --accent:#b8321f; --accent-ink:#ffffff; --mark:#fde7a8; --mark-ink:#1d2640;
  --chip:#eceef1; --chip-active:#1d2640; --chip-active-ink:#ffffff; --gold:#b07700;
  --diagram:#fbfbf9;
}
@media (prefers-color-scheme: dark){
  :root{
    --bg:#131722; --surface:#1b202d; --ink:#eceef4; --muted:#a2aabc; --line:#2c3344;
    --accent:#f0765f; --accent-ink:#1b1f2a; --mark:#f1bd4a; --mark-ink:#1b1f2a;
    --chip:#262c3b; --chip-active:#eceef4; --chip-active-ink:#1b202d; --gold:#f1bd4a;
    --diagram:#f3f4f6;
  }
}
*{box-sizing:border-box}
html,body{margin:0}
body{background:var(--bg);color:var(--ink);font:16px/1.55 Figtree,system-ui,-apple-system,"Segoe UI",sans-serif;-webkit-font-smoothing:antialiased}
button{font:inherit;color:inherit}
:focus-visible{outline:2px solid var(--accent);outline-offset:2px}

.app{display:grid;grid-template-columns:270px 1fr;min-height:100vh}
.side{border-right:1px solid var(--line);padding:24px 16px;position:sticky;top:0;height:100vh;overflow-y:auto;background:var(--surface)}
.brand{display:block;font-family:"Young Serif",Georgia,serif;font-size:1.35rem;line-height:1.15;color:var(--ink);text-decoration:none;margin-bottom:6px}
.brand span{color:var(--accent)}
.side-note{font-size:.8rem;color:var(--muted);margin:0 0 16px}
#nav{display:flex;flex-direction:column;gap:2px}
#nav .group{font-size:.7rem;letter-spacing:.12em;text-transform:uppercase;color:var(--muted);font-weight:700;margin:14px 8px 4px}
#nav a{display:grid;grid-template-columns:22px 1fr auto;align-items:baseline;gap:6px;padding:6px 8px;border-radius:6px;color:var(--ink);text-decoration:none;font-size:.9rem}
#nav a:hover{background:var(--chip)}
#nav a[aria-current="page"]{background:var(--chip-active);color:var(--chip-active-ink)}
#nav .n{font-variant-numeric:tabular-nums;color:var(--muted);font-size:.8rem}
#nav a[aria-current="page"] .n{color:inherit;opacity:.7}
#nav .star{color:var(--gold);font-size:.75rem}
#nav .done{font-size:.75rem;color:#2f8a4f}
.mobile-pick{display:none}
.play-link{display:block;margin:0 0 14px;padding:9px 12px;border-radius:8px;background:var(--accent);color:var(--accent-ink);text-decoration:none;font-weight:600;font-size:.9rem;text-align:center}

.main{padding:28px clamp(16px,3vw,40px) 40px;display:flex;flex-direction:column;gap:20px;min-width:0}
.rule-head{max-width:80ch}
.eyebrow{display:flex;gap:10px;align-items:center;font-size:.85rem;color:var(--muted);font-variant-numeric:tabular-nums}
.badge{font-size:.7rem;font-weight:700;letter-spacing:.08em;text-transform:uppercase;color:var(--gold);border:1px solid currentColor;padding:1px 7px;border-radius:4px}
h1{font-family:"Young Serif",Georgia,serif;font-weight:400;font-size:clamp(1.7rem,3.4vw,2.4rem);line-height:1.12;margin:6px 0 8px;text-wrap:balance}
.tip{margin:0;color:var(--muted);font-size:1.05rem;max-width:70ch}

.stage{display:grid;grid-template-columns:minmax(0,1.35fr) minmax(320px,1fr);gap:20px;align-items:start}
.diagram-wrap{background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:14px;position:sticky;top:16px}
.diagram{background:var(--diagram);border-radius:8px;padding:14px;overflow:auto;min-height:220px;display:flex;align-items:center;justify-content:center}
.diagram svg{max-width:100%;height:auto;max-height:62vh}
.diagram-hint{margin:10px 2px 0;font-size:.8rem;color:var(--muted)}
.diagram .err{color:#b8321f;font-size:.9rem}

/* highlight state */
.diagram g.node,.diagram .edgePaths path,.diagram .flowchart-link,.diagram .edgeLabel{transition:opacity .25s ease}
.diagram.has-sel g.node{opacity:.4}
.diagram.has-sel .edgePaths path,.diagram.has-sel .flowchart-link,.diagram.has-sel .edgeLabel,.diagram.has-sel marker{opacity:.45}
.diagram.has-sel g.node.hl{opacity:1}
.diagram g.node.hl rect,.diagram g.node.hl polygon,.diagram g.node.hl circle,.diagram g.node.hl path{stroke:#b8321f !important;stroke-width:3px !important;fill:#fff3d1 !important}
@media (prefers-reduced-motion: reduce){.diagram g.node{transition:none}}

.practice{background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:16px;display:flex;flex-direction:column;gap:14px}
.practice-top{display:flex;justify-content:space-between;align-items:center;gap:10px;flex-wrap:wrap}
.practice h2{font-size:.75rem;letter-spacing:.12em;text-transform:uppercase;color:var(--muted);margin:0}
.toggle{font-size:.85rem;color:var(--muted);display:flex;gap:6px;align-items:center;cursor:pointer}
.ex-list{display:flex;flex-direction:column;gap:6px}
.ex-btn{display:grid;grid-template-columns:22px 1fr;gap:8px;text-align:left;background:var(--chip);border:1px solid transparent;border-radius:8px;padding:9px 11px;cursor:pointer;line-height:1.35}
.ex-btn:hover{border-color:var(--line)}
.ex-btn .i{font-variant-numeric:tabular-nums;color:var(--muted);font-size:.85rem}
.ex-btn[aria-selected="true"]{background:var(--chip-active);color:var(--chip-active-ink)}
.ex-btn[aria-selected="true"] .i{color:inherit;opacity:.7}
.ex-btn mark{background:none;color:inherit;font-weight:700;padding:0}

.ex-card{border-top:1px solid var(--line);padding-top:14px;display:flex;flex-direction:column;gap:4px}
.lang{margin:0;font-size:.7rem;letter-spacing:.12em;text-transform:uppercase;color:var(--muted);font-weight:700}
.es{font-family:"Young Serif",Georgia,serif;font-size:clamp(1.4rem,2.6vw,1.8rem);line-height:1.25;margin:0 0 10px}
.en{all:unset;display:block;font-size:1.15rem;margin:0 0 6px;cursor:default}
.en.hidden{cursor:pointer;color:var(--muted);border:1px dashed var(--line);border-radius:6px;padding:6px 10px;font-size:.95rem}
mark{background:var(--mark);color:var(--mark-ink);padding:0 .15em;border-radius:3px}
.lit{margin:0;font-size:.9rem;color:var(--muted);font-style:italic}
.lit:empty{display:none}
.note{margin:8px 0 0;padding:10px 12px;background:var(--bg);border-radius:8px;font-size:.95rem}
.ex-actions{display:flex;gap:8px;margin-top:12px;align-items:center}
.spacer{flex:1}
.btn{background:var(--accent);color:var(--accent-ink);border:0;border-radius:8px;padding:8px 14px;font-weight:600;cursor:pointer}
.btn.ghost{background:transparent;color:var(--ink);border:1px solid var(--line)}
.btn:disabled{opacity:.4;cursor:default}
.keys{margin:0;font-size:.8rem;color:var(--muted)}

.rule-foot{display:flex;align-items:center;gap:12px;justify-content:space-between;border-top:1px solid var(--line);padding-top:16px}
.progress{font-size:.85rem;color:var(--muted);font-variant-numeric:tabular-nums}

@media (max-width:1150px){
  .stage{grid-template-columns:1fr}
  .diagram-wrap{position:static}
  .diagram svg{max-height:none}
}
@media (max-width:860px){
  .app{grid-template-columns:1fr}
  .side{position:static;height:auto;border-right:0;border-bottom:1px solid var(--line);padding:14px 16px}
  .side-note,#nav{display:none}
  .play-link{margin:10px 0 0}
  .mobile-pick{display:flex;flex-direction:column;gap:4px;font-size:.75rem;color:var(--muted);margin-top:8px}
  .mobile-pick select{font:inherit;font-size:1rem;padding:8px;border-radius:8px;border:1px solid var(--line);background:var(--bg);color:var(--ink)}
  .main{padding-top:18px}
  .keys{display:none}
  .rule-foot{flex-wrap:wrap}
  .progress{order:-1;width:100%;text-align:center}
}